The present invention relates to an LED, in the case of which the at least one LED die is arranged on a LED PCB with a die attach, and the LED PCB has on the side opposite to the LED die electrical rear side contacts, which if appropriate are as plug-in contacts. It further relates to a LED light source having one or more LEDs, of the kind mentioned above, arranged on a board or on a plug, wherein the board has contact surfaces or the plug has contacts, with which the LEDs are contacted.
LED light sources normally have the following structure:
The LED die is applied to a contact surface (e.g. conductor path) of an LED PCB by means of a die attach (PCB=printed circuit board; the term die attach includes both a die adhesive connection and also a solder connection). Together with the rear side contacts of the LED PCB this arrangement represents a self-contained LED lamp. This LED lamp is assembled onto a board by means of a mounting technology (e.g. SMT), which board is then optionally connected with a cooling body. Optionally, the lamp may be fixed and contacted in a lamp socket. Instead of on a board, the LED can also be assembled on a plug.
In order to realize LED applications having high brightness, ever stronger high power LEDs are put to use, already even with an operating power of more than 1 Wel. The chip area of these LEDs is at the present time in the region of 1 mm2. There is a trend that in future the operating power per LED will further increase, which on the one hand will be achieved by means of larger semiconductors and on the other hand by means of higher current densities. In particular the latter parameter has the effect that the power density of LEDs of at present maximally 1-2 Wel/mm2 will in future increase above 4 Wel/mm2.
However, for the discharge of the waste heat appropriate arrangements are to be realized, which allow the heat to be sufficiently discharged from the semiconductor.
Too great warming during the operation of the LED leads to component destruction. For this reason, during the operation of the LED, it must be ensured that the temperature at the barrier layer of the p-n junction in the LED does not rise above typically 130° C. This can occur during the operation of the LED insofar as only a part of the electrical power taken up by the component is converted to light, whilst the other part is converted to heat. (At the present time, the power efficiency of LEDs is less than 10%). The operating parameters of LEDs are thus to be selected in dependence upon the manner of assembly, the installation and environmental conditions, such that the barrier layer temperature always remains below 130° C.
In the subject invention, arrangements are presented which can discharge the waste heat of LEDs with such efficiency that power densities of over 2 Wel/mm2 can be discharged.
In order to efficiently discharge the waste heat, the thermal resistance of the arrangement must be optimized. If the heat can be transferred to the LED carrier without a great temperature difference, the barrier layer remains below the maximum permitted temperature. The significant physical parameter is thus the thermal resistance, measured in K/W.
Arrangements and structures such as are at the present time state of the art for high power LEDs have in optimized arrangements typically a thermal resistance of more than 20 K/W (interface junction to LED carrier material). This means that the temperature difference between the LED carrier and the active zone of the LED—in operation at 5 Wel—is more than 100 K. Starting from a maximum permissible barrier layer temperature for long term applications of 130° C., this means that employment is impossible at temperatures above 30° C. and thus this LED is unsuitable for many technical applications (automobiles, transport).